Lightning-arrester.



R. B. INGRAM.

LIGHTNING ARRESTER.

APPLICATION FILED JUNE 25, 1906.

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ATTORNEY R. B. INGRAM. LIGHTNING ARRESTER.

I APPLIGATIQN FILED 313N325, 1906.

Patented Jan. 2, 1912.

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APPLICATION FILED JUNE 25, 1906.

Patented Jan. 2,-191'2'] 3 SHEETSSHEET 3.

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RALPH B. INGRAM, OF WILKINSBURG, YENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC &. MANUFACTURING COMPANY, A. CORPORATION'OF PENNSYLVANIA.

LIGHTNING-ABRESTER.

Specification of Letters Patent.

Patente Jan. 2,1912.

Application filed June 25, 1906. Serial No. 323,361.

for protecting electric .circuits and apparatus from 1n ury by' reason of lightning discharges and other static disturbances as well as dynamo currents, of high potential which tend to follow the paths established by static discharges.

The object of my invention is to provide means for insuring an approximately constant ratio between the aggregate air-gap of a protective device and its critical voltage, that is, the lowest voltage at which a discharge will occur. t

A well known form of protective device or lightning arrester comprises a series of air-gaps formed by a plurality of conducting blocks located at short distances from each other. \Vhen a device of this kind is adapted for the protection of relatively high voltage lines by increasing the number,

of air-s raps. it has been observed that, while the aggregate air-gap is increased, its voltage-sustaining or withstanding power is not correspondingly increased. This discrepancy may be attributed to a condenser action which takes place betweenthe several conducting blocks and the earth. Under ordinary circumstances. this condition is undesirable, and, in order to avoid it, I provide a. shield which destroys the condenser action between the conducting units and the ground and establishes a substantially constant ratio between the aggregate length of the air-gap in the protective device and its critical voltage.

In the accompanying drawings Figure 1 is a view partially in front elevation and partiallv in section and Fig. 2 a diagrammatic view of a protective device constructed in accordance with my invention. Fig. 3 is a detail view of a group of units such as are shown in Fig. 1-, and Fig. 4 is a diagranr matic view of a protective device employed between two line conductors neither of which is grounded. Figs. 5 and 6 are diagrammatic views, at right angles to each other, of a modified shield structure which is adapted for use with high voltagelines.

Fig. 7 shows a set of curves obtained by p plotting the results of tests made on a lightning arrester by varying the number of units of which itis comprisedand measuring the voltage at which an arc is estab lished, withand without the shield of my invention. Fig. 8 is a curve obtained by varying the number of units, ofapredetermined series, which are protected by the shield and measuring the voltage at which an are is established across the units for..

each variation.

The shield itself ma comprise a pine or conducting material or a conductor of any suitable form which may be electrically. connected to the line to be protected, and be insulated from the units by a suitable dielec tric, such as an insulating plate or tube, and

which extends, over or in proximity to a portion of the unitsfcomprising the device, If the device itself is mounted on a wall i near an objectwhicb isgrourided, the shield .is preferably located between the units of the lightning arrester and r the nearest grounded object. V

Referring to Figs. 1, 2, and 3' of the draw:

ings, an electric line conductor 'l' is 'pro tected from lightning or other static disturbances, by means of a lightning arrester 2, which comprises a series ,of blocks 3 of conducting material separated by relatively short air gaps 4. One end of the series'of" conducting units is connected to line conductor 1 while the opposite end of the series is grounded through a suitable resistance 5 The lightning arrester 2 is provided with a. shield 6 which'comprises a plate 7 of in-" sulating material and a conducting plate..8.

The conducting plate 8 of the shield (his connected to the lineconductor 1 and extends over, or in proximity to a number of the units 3, which may bedefinitely [iredetermined as hereinafter pointed out, the

conducting platebeing-separated from the 106 units by the insulating plate 7. I In Figs. 5 tel 4i 6, a modified form shield is illustrated comprising a plurality of conductors 9 and 10 that areconnected, in

multiple arc .and are separated from 'the 10.

conducting blocks 3 by insulating tubes 1111 and-12.. This structure is of-special vantage for use in connection with the pro tection of high voltage lines, since it is relatively easy to provide an insulating tube capable of withstanding very high voltages.

' Reference may now be had to Fig. '7, curve A of which is obtained by varying the number of units 3 of which the lightnin arrester is composed and measuring for eac variation, without the use of the shield 6, the voltage at which an arc may be established from the line conductor to the ground. It will be observed that the first part of this curve which represents the conditions for the protection of lpw voltage lines is nearly straight, indicating that the critical voltage increases substantially in the same ratio as the aggregate length of the air-gap, while,

as the number of units-is increased for the protection of the higher voltage circuits, the curve is materially'flattened, indicating that when the aggregate air-gap is relatively long the critical voltage is not correspondi ingly increased.

If a convenient number of units be taken and a shield, such as that already described, be'so applied as to cover a varying number of unistfroih the end which is connected to the inecbnductor and a breakdown volt-' age be obtained for each variation, the results will be indicated by a curve, similar to curve C of Fig. 6, having a peak that indicates' the number of units which should be covered by the shield in order that the critical voltage may be maximum. If the total number of units in the lightning arrester be varied and, for each-variation, a curve be obtained similar to the curve C, (Fig. 8), and if then a curve be drawn through the peaks of the several curves; the

number of units which should be covered in a lightning arrester having any given aggregate air-gap (as indicated by the-number i of uni s of which the device is composed) the reduction of the critical voltage will be.

effected if the shield is arranged adjacent to all, or nearly all, of the conductingblocks. Curve D of Fig. 7 clearly indicates the effect of arranging the shield inthe manner just described.

In some cases it is desirable to decrease the critical voltage, making it easier for an g are to be established across the gaps. This result is accomplished by the arrangement disclosed by Patent No. 571,099, granted to the Westinghouse Electric & Manufac turing Co. November 10; 1896, on an application filed by Charles E. Skinner May 21, 1896., and forms no part of my present invention.

Tests have shown that with a shield of this kind, a constant ratio .between the breakdown voltage and the aggregate length of air-gap is substantially maintained throughout the complete range of voltage which I have been able to obtain.

- According to my present invention, it is desired to abrogate the forces which tend to reduce the .voltage sustaining power of a predetermined aggregate air-gap in protective apparatus,"and inorder that this resultmay be accomplishedit is essential that the shield be adjacent to only a part of the condu cting blocks or cylinders of which the apparatus is composed. As clearly shown in curve C-of Fig. 8, the effect of the shield is not only useless but actually'detrimental to the operation of the device if more than a predetermined portion of the cylinders are covered.

When the protective devices similar to the lightning arresters already described are connected'between two circuit conductors, neither of which is grounded, for preventing static disturbances, the most advantageous arrangement of the shield comprises, as illustrated in Fig. 4: two similar conduct- .ing members which are severally connected to'the line conductors and which eatend for a short distance toward each other, near the units comprising the protective device that are adjacent to the line conductors.

Obviously, the voltage strains are greater near the end of the plate or shield which is farthest from the line conductor to Which it is connected, so that if air is used as a dielectric the end of the plate should be more widely separated from the conducting units as shown in Fig. 4. 1 It is conceivable that changes in the size and arrangement of parts may beefi'ected in the apparatus illustrated, without departing from the spirit of my invention, and I desire that only such limitations be imposed as are indicated in the appended claims.

' I claim as my invention: 1. In a lightning arrester, the combination with aseries of blocks of conducting material which are separated by relatively short air-gaps, of means for maintaining a substantially constant ratio between the length of the aggregate air-gap and the voltage at which an arc willbe established across the gaps.

2. In a lightning arrester, the combination with a series of blocks of conducting material which ,areseparated by relatively "short air gaps, of a conductor which -is connectedto an end block of the series and extends close to such a predetermined number of the blocks as to maintain a substantially constant ratio between the length of the aggregate air-gap and the critical voltage of the arrester.

3. In a lightning arrester, the combination with an electric line conductor, and

- conducting members which form a series of air-gaps between the line and the ground,

of a conducting shield disposed adjacent to a predetermined portion of the series of airgaps whereby the critical voltage of the arrester is maximum.

4. The combination with a series of blocks of conducting material which are separated by relatively short air-gaps, of a conductor which is connected to an end block of the series and extends close to a predetermined number, less than half of the series, of the blocks adjacent to said end blocle In testimony whereof, I have hereunto subscribed my name this 23rd day of June,

I RALPH B. INGRAM.

Witnesses:

GIRARD B. RosENBLArr, BIRNEY HINES. 

